Hydraulically effected change of force which is effective counter to a spring makes possible quick opening and closing of the reversing valve in one stroke.
1. Field of the Invention
The present invention relates to a switch valve, reversing valve, or change-over valve, for a combination meter having a main meter acted upon by a main flow, and an auxiliary meter acted upon by an auxiliary flow; a closure element is movable in the axial direction within the reversing valve housing, and is adjustable directly and from time to time by a hydraulic adjustment 7 member by the flow pressure of the measured liquid and by the pressure of the force of a spring element which is effective counter to the flow pressure of the measuring liquid; the main flow is greatly throttled in the last closing phase of the closure element.
2. Description of the Prior Art
A reversing valve of this general type is disclosed by German Patent No. 1960735 Schmidt and British Patent No. 1,331,973 corresponding thereto, each belonging to the assignee of the present invention. The closure element of the known reversing valve is movable directly by the pressure of the main flow and two spring elements of different strength effective counter thereto. The strong spring element is effective only in the direct closing range. If the closure element has left this direct closing range, the strong spring force is mechanically eliminated as a result of the constructive configuration of the reversing valve, and only the weak spring element now acts counter to the flow pressure with a relatively flat characteristic curve. A hydraulic adjustment member in the form of a hydraulic pusher is additionally associated with the closure element; the working chamber of the pusher is continually only acted upon by the pressure of the main flow, so that the hydraulic pusher, and hence during closing also the closure element, are continuously subjected to the differential pressure of the measured liquid ahead of and behind the closure element and the spring elements effective counter thereto. During opening of the closure element, the hydraulic pusher is lifted therefrom, moves after the opening as a result of decrease of the pressure difference in the direction of the closure element, and takes the latter along counter to, and dependent upon, the flow pressure of the measured liquid, until after it has covered a predetermined distance, the strong spring element becomes effective and suddenly presses the closure element into the closed position. With the known reversing valve, the inlet for the auxiliary flow is located in the region of the inlet for the main flow. Downstream from the inlet of the auxiliary flow, the closure element has an annular plate or disc on its outer periphery; this plate or disc cooperates with a throttle ring on the inner side of the housing of the reversing valve in the manner of a throttle element. The spacing between the plate or disc and the throttle ring forms an annular throttle opening. If only the auxiliary meter is operating, the plate or disc is located upstream ahead of the throttle ring; when both main and auxiliary meters are operating, the plate or disc is located downstream after the throttle ring. When the closure element is moved in the direction of the closed position, the force of the weak spring element on the one hand, and a force effective counter thereto on the other hand, are effective, which corresponds to the pressure loss resulting from the throttling between the plate or disc and the throttle element, with respect to the entire cross section of the closure element as enlarged by the plate or disc. The spacing or distance between the plate or disc and the throttle ring is such that a further movement of the closure element in the closed direction occurs only when the entire flow of the main and auxiliary meters is decreased below the valve which was necessary for opening. If this is the case, the plate or disc approaches the throttle ring, the strong spring element is effective in addition to the weak spring element and thereby increases the closing force in a sudden manner, the disc or plate passes the throttle ring, the free through-passage cross section is suddenly expanded, and the force effective counter to the spring elements thereby decreases abruptly and makes possible an accelerated closing of the reversing valve. The opening of the reversing valve is likewise effected in a sudden manner, since a throttling immediately occurs between the plate or disc and the throttle ring with a movement of the closure element, so that the closure element passes the throttle ring with its plate or disc positively by means of the resulting increase of the pressure difference. The pressure relief in the open position is attained by eliminating the force of the strong spring element, and by increasing the effective pressure surface of the closure element by the surface of the annular plate or disc. The known reversing switch operates completely satisfactorily with respect to the reversing points of the main meter during rising and dropping load, and the permissible measuring error range is not fully utilized during the reversing.
When using only one spring, it must be strong enough that the closure element remains in the closed position until the auxiliary meter produces a through-flow intensity which is greater than the lower measuring region limit of the main meter in order to also maintain the limits or error during the reversal. However, the force of the strong spring is still further increased during opening, which additionally counters an effective pressure relief. If this is to occur via an enlargement of the cross section of the closure element by means of the plate or disc of the throttle element, then the pressure relief after the opening is slight with a plate or disc which is kept small, and the necessity of a very small gap for opening and closing between the plate or disc and the throttle ring is disadvantageous. Although an enlargement of the plate or disc produces a better pressure relief after the opening, a larger and heavier housing is required, and the cross section of the annular gap cannot be arbitrarily enlarged because of the necessity for maintaining the reversing points, since the annular gap is correspondingly longer in the peripheral direction as a consequence of the greater circumference of the plate or disc. This in turn requires a narrower annular gap, which promotes the entry and deposition of foreign bodies, which prevent the free movement of the closure element and also block the latter. Already with unavoidable, smaller deposits on the large (relative to the cross section) surface of such annular gaps, clear cross sectional reductions result, which in turn result in a disadvantageous shifting of the reversing points.